Labeled and purified host cell protein, RNA, and DNA are hydrolyzes by Bdellovibrio extracellular enzymes. The hydrolyzed protein or nucleic acids were added to a host free medium and inoculated with Bdellovibrio. The amount of uptake and TCA precipitable counts in stationary phase cells was then determined. From these studies it has been demonstrated that Bdellovibrio extracellular enzymes hydrolyze host macromolecules to products which are subsequently used in the biosynthetic pathways of Bdellovibrio. It is also suggested that Bdellovibrio cannot synthesize their own nucleotide bases, since neither C14 glycine nor H3 aspartic acid was incorporated into hot TCA soluble material. A variety of temperature-sensitive mutants of H-D B. bacteriovorus 109D were selecte$ following ethylmethane sulfate mutagenesis. Representatives of these mutants were then characterized by phase-contrast and electron microscopy, temperature-shifted on-step growth experiments, attachment kinetic and macromolecular capabilities.